Grade 10 power mechanics Motor Vehicle Systems – Road Wheels Notes

1. Identify and outline sub-sub-strands:
   • Functions of wheels in a vehicle
   • Types of tires used in vehicles
   • Types of ply orientation in tires
   • Interpretation of tire specifications in relation to road safety
   • Importance of tires in vehicle operations
2. Explain the functions of wheels in a vehicle.
3. Identify types of tires used in vehicles.
4. Illustrate types of ply orientation used on vehicle tires.
5. Interpret specifications on tire sidewalls in relation to road safety.
6. Appreciate the role of tires in vehicle operations.

1. Functions of wheels

• Support the vehicle's weight (carry load of chassis, passengers, goods).
• Provide mounting surface for the tyre so the tyre can contact the road.
• Transmit driving force and braking force between tyre and axle.
• Help maintain steering and directional stability with correct alignment.
• Work with tyres and suspension to absorb shocks from rough roads.

2. Types of tyres (tires)

Common tyre types you will see on Kenyan roads:

• Radial tyres — most passenger cars: flexible sidewall, steel belts under tread; better fuel economy and ride comfort.
• Bias-belted tyres — older design, some commercial vehicles; stronger sidewalls.
• Tube-type vs. tubeless — modern cars use tubeless tyres; older rims or some trucks use tube-type.
• All-terrain / Mud-terrain — used on 4x4s and pickups to handle rough Kenyan roads and farms.
• Highway / City tyres — designed for long distances on paved roads (matatus, buses).
• Specialised tyres — winter tyres (rare in Kenya), run-flat tyres (on some cars).

3. Ply orientation — illustrations

How the cords (plies) are arranged inside a tyre affects strength and handling.

4. Reading tyre sidewall markings (safety)

Example marking: 205/55 R16 91V

• 205 = tyre width in millimetres (distance across the tread).
• 55 = aspect ratio (sidewall height is 55% of width).
• R = radial construction (most modern tyres). If "D" = diagonal/bias.
• 16 = rim diameter in inches (the wheel the tyre fits).
• 91 = load index (lookup table gives max load per tyre). Example 91 ≈ 615 kg per tyre.
• V = speed rating (maximum safe speed for that tyre when correctly loaded and inflated). V ≈ 240 km/h (do not drive at that speed on public roads).

Other important markings:

• DOT followed by codes — shows tyre meets safety standards and includes date of manufacture (last 4 digits: week and year, e.g., 2319 = 23rd week of 2019).
• Max Load / Max Pressure — never exceed these values.
• TWI — tread wear indicators show when tyre depth reaches minimum.

Safety tips from markings: Always fit the correct rim size and load/speed rated tyres for your vehicle. Do not use a tyre with a lower load rating than recommended by the vehicle maker.

5. Why tyres are important to vehicle operations

• Traction and braking — good tyres shorten stopping distance, especially on wet or rough Kenyan roads.
• Handling and stability — correct tyres and pressure make steering predictable and safe.
• Fuel economy — under-inflated tyres increase rolling resistance and raise fuel use.
• Comfort and load carrying — tyres absorb shocks and carry passengers/goods safely.
• Safety — worn or damaged tyres increase risk of blowouts, skids, and accidents.

6. Maintenance — practical (Kenyan context)

• Check tyre pressure weekly or before long trips. Use the pressure recommended on the vehicle door sticker or owner’s manual (not the number on the tyre).
• Inspect tyres for cuts, bulges, nails, stones stuck in tread — common hazards on Kenyan roads with potholes.
• Measure tread depth — replace when near 1.6 mm or when TWI shows. In wet seasons, replace earlier for better grip.
• Rotate tyres every 8,000–10,000 km to ensure even wear (matatus and commercial vehicles often rotate more often due to heavier loads).
• Ensure wheel nuts are tightened to correct torque and check wheel alignment and balancing after hitting big potholes.
• Avoid overloading the vehicle — excess weight stresses tyres and increases chance of failure on bad roads.

Suggested learning experiences (practical)

1. At a school workshop or on a supervised trip to a local garage:
   • Identify tyre markings on tyres of a car and record the numbers (width, aspect, rim size, load/speed rating).
   • Use a tread depth gauge or a ruler to measure tread on each tyre and mark tyres that need replacement.
   • Practice checking tyre pressure with a gauge and inflator; record PSI before and after.
2. Class demonstration: show bias vs radial ply diagrams and explain why radials are common on cars.
3. Group activity: make a simple poster listing daily tyre checks and display it near the school vehicles.

Appreciation

Tyres are the only contact between a vehicle and the road. Good tyres and correct maintenance keep passengers safe, reduce vehicle running costs, and improve comfort. As future drivers or mechanics, regular tyre checks and correct selection are key responsibilities.

1. What does 205/55 R16 mean? (briefly write each part).
2. Name two tyre types used on Kenyan roads and one advantage of each.
3. List three simple tyre maintenance actions you should do before a long trip.